Geoffrey claimed, in the introduction to his book, merely to be translating an old British-language book brought out of Brittany or Wales by Walter, archdeacon of Oxford. But, if Walter gave Geoffrey any written material, it could scarcely have been the only source and it could not have borne much resemblance to the Historia which has multiple literary sources – classical, biblical, and historical.

The Historia’s detailed and comprehensive narrative, is unique and most of what it contains cannot be confirmed by any other document. It is a well planned and structured literary composition with a beginning, climax and end with a narrative thread which allows this accomplished storyteller to insert entertaining episodes to enliven the whole, so that the work bears all the hallmarks of single authorship, that of Geoffrey of Monmouth.

In his dedication, Geoffrey he says that his purpose in writing (or translating) is to give an account of British history before the coming of the English, a period upon which English and Norman historians could shed little light. Geoffrey, having spotted a gap in the market, met the challenge by brilliantly creating an imaginary history, using and adapting whatever genuine sources he could, drawing on traditional Welsh and British folktales and legends combined with his own reading, and devising the rest. He writes sometimes ironically, sometimes with tongue-in-cheek humour, but often with conviction about contemporary concerns – the futility of fraternal strife and civil war, about heroism and treachery, about kingship, justice and freedom, and throughout runs a belief in the moral qualities of governance. He aspires to write like a contemporary historian; ‘forger’ he may have been but he writes of underlying truths.

Most of all Geoffrey reflects in the structure and ambiguities of his book the unifying themes of native, Welsh, legendary history, which has to do with the unity of Britain and the sovereignty of the British, their loss of hegemony and of unity, and the prophesied restoration of all these one future day. Geoffrey did not create the Arthurian myth, but he gave it its most coherent expression and a new status in its learned Latin context.